Regarding the air pump. Maybe this will help. http://www.mbpumps.com/

The guy does stand behind his pumps (in my experience).

I wish I knew about this before I paid the dealer over $1,500 three years ago for a Nipondenso air pump. One thing I learned was that any Japanese part that's connected to a German-designed car is super expensive to buy from the dealer. My bearings went out on the old pump.

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1993 400E, 256,000 miles (totaled)
1994 E420, 200,000+ miles
1995 E420, 201,000 miles